1. Field of the Invention
The present invention is directed to a novel system for transporting articles into and out of a furnace, and specifically to a novel non-reactive system for transporting and holding articles in a high temperature environment.
2. Description of the Prior Art
Various systems have been devised to move articles through furnaces. These systems usually have been directed to continuous furnace operations, that is, operations in which the furnace conditions are maintained, and articles that require elevated temperature processing are continuously moved through the furnace. Furthermore, the systems typically are directed to providing solutions to problems that peculiar to the processing methods.
One such system is set forth in U.S. Pat. No. 3,825,873 to Herron et al. This system sets forth a strand annealing method for thin walled metal tubes. The system utilizes copper or aluminum wheels with electrical contact material in the form of brushes to provide the required electrical connection at the high temperatures.
U.S. Pat. No. 5,848,890 to McCormick dated Dec. 15, 1998 is directed to an improved device for transporting items through a furnace. The device could be used as a pusher type transporting system or as a system to move articles through the furnace continuously. The device utilizes carriers that operate in channels that serve to protect the carriers from the furnace atmosphere. Insulating materials can be included in the channels to provide additional isolation from the furnace atmosphere. The carriers are made from ceramic, intermetallic material or graphite. The carriers are moved through the channels by any conventional means such as rollers or by pushing.
U.S. Pat. No. 5,042,423 to Wilkinson dated Aug. 27, 1991 is directed to a carrier for moving silicon wafers through a continuous CVD reactor. The carriers are graphite or are graphite-coated vessels that hold wafers and facilitate the coating of the wafers as they are moved through the reactor. The carriers are actually transported through the vessel on rails.
Activated Diffusion Healing (ADH) and brazing are processes used in the refurbishment of turbine engine components. While there are differences in the processes, both processes accomplish repairs of damaged portions of turbine engine hardware by applying repair material that has a lower melting temperature than the component base material. The damaged portions are removed and the removed material is replaced by repair material. The repair material is incorporated into the component base material by heating both the component and the repair material to a temperature above the melting temperature of the repair material, yet below the melting temperature of the component. The primary difference between brazing and ADH is in the materials used in repair and the temperature of repair. Brazing alloys typically are lower melting and retain this low melting characteristic even after incorporation into the component. Furthermore, braze repairs usually have mechanical properties that are different from the mechanical properties of the component base material. ADH is comprised of a plurality of alloys with different melting temperatures at least one of which has a high diffusion coefficient and is below the melting temperature of the components. As the ADH material is heated, it melts and is incorporated into the alloy. However, after an appropriate heat treatment, the low melting component diffuses into adjacent substrate, and the repaired area comprised of the ADH alloy has a melting temperature that is close to the melting temperature of the component. The repaired area also has mechanical properties that are very similar to the base material of the component. Details of brazing and the ADH process may be found in U.S. Pat. Nos. 4,830,934, 5,240,491 and 5,666,643, assigned to the assignee of the present invention, the contents of which are incorporated herein by reference.
Despite the differences between the two processes, both share common problems in processing the turbine components under repair in furnaces at high temperatures. A plurality of parts typically are loaded into the furnace on carriers or trays. The carriers are made from various materials, but typically include a metallic component which may have an overlying protective coating. Metallic components typically have infirmities for carrier applications at high temperature. First, only certain metals have melting temperatures that are sufficiently high to permit their use in these applications. At these elevated temperatures, components made from these metals typically experience a lowering of their yield strength. Additionally, there is a tendency for some of the materials used in the processes, particularly the ADH processes, to be transferred onto the metallic components. This material can degrade the mechanical performance of these components as it builds up on surfaces in which clearances must be maintained. In such applications, binding becomes a problem. For support surfaces, the processing materials tend to build up and are difficult to remove as they diffuse into the surfaces. For coated metal surfaces, the removal of residual ADH or braze materials frequently also results in the removal of the protective coating. As a result, the processing materials not only degrade the support surfaces, but can contaminate parts processed at a later time, again by diffusion.
While both intermetallics and ceramics have been combined with certain metal parts, these materials suffer from certain infirmities. Both tend to be brittle and can crack when impacted, such as if a large part shifts. While processing material readily can be removed from ceramics, intermetallics have the same degradation problem as do metallic materials.
Another solution has been to load parts into ceramic trays and insert them into a furnace or oven without the use of aids such as wheels. Such an apparatus can be used successfully when the parts are small and the resulting weights are light, but movement can be cumbersome and slow. Additionally, the ceramic trays are subject to fracture if there is a shifting of the parts.
What is needed is a device that can be used to facilitate the ingress and egress of a load of turbine engine parts into a high temperature furnace or oven to accomplish brazing or ADH. The device must be capable of supporting the parts at the elevated temperatures used to accomplish ADH and brazing and should not be adversely affected by materials utilized in the ADH or brazing process.
The present invention provides a transporting device for use in transferring parts and holding parts in high temperature environments above 1600xc2x0 F. in controlled atmospheres. The transporting device is specifically designed for use in high temperature environments for rapid furnace ingress and egress of articles and to hold the articles during the heat treatment.
The device of the present invention is designed so as not to be reactive with either the furnace atmosphere or with the components loaded onto the transporting device. The device is comprised of a plurality of nonmetallic rollers that can withstand the high temperatures of the furnace without being adversely affected by the furnace atmosphere. Each roller has a central aperture for receiving a roller bearing, the roller bearing also being able to withstand high temperatures without being adversely affected by the furnace atmosphere. The roller bearing also has a central aperture. An attaching means extends through the roller and the roller bearing and attaches the roller containing the bearing to a nonmetallic support surface. The roller bearings are attached to the support surface by mounting means. The nonmetallic support surface is capable of supporting a load of turbine engine components as they undergo brazing or ADH at temperatures of at least about 1800xc2x0 F. (982xc2x0 C.) without yielding.
The device is designed to support a plurality of turbine engine components such as high pressure turbine nozzles. At least one high temperature spacing means is positioned between the support surface and each roller to prevent the roller from binding against the support surface. An optional high temperature spacing means is positioned between the attaching means and the roller. Each spacing means has a central aperture alignable with and corresponding to the central aperture of the roller and the central aperture of the bearing for receiving the attaching means. The transporting device also includes at least one non-metallic housing for receiving a temperature monitoring means. The at least one housing is positioned adjacent to the non-metallic support surface so that an accurate reading of the temperature of the parts located on the support surface can be obtained. The housing is designed so that a temperature monitoring means, such as a thermocouple, can readily be activated. The at least one housing includes at least one opening, and usually includes a plurality of openings to prevent the build-up of heat within the housing, facilitating free circulation of furnace atmosphere within the housing so that the temperature within the housing can provide an accurate representation of the temperature of the parts on the support surface.
An advantage of the present invention is that it can withstand the high temperatures and non-oxidizing environments in which ADH and brazing occurs, so that there is no deterioration of the transporting device. Further, because the material comprising the transporter is non-reactive with the materials used in the ADH and brazing processes, transporter contact with such ADH or brazing materials will not degrade the transporter. In fact, at the conclusion of a repair cycle, any ADH or brazing material can be readily removed from the transporter without the need for aggressive cleaning methods that abrade the surface, such as grinding.
Another advantage of the present invention is that the material utilized in the transporter is non-brittle and undergoes no decrease in mechanical strength at elevated temperatures. As a result, the transporter can be loaded at or near room temperature and placed in a furnace with little consideration of the effects of the load at elevated temperature on the transporter, as the transporter will not warp or distort.
Another advantage of the present invention is that the constituent parts of the transporter have low thermal expansion coefficient and high thermal shock resistance. Because of the low thermal expansion coefficient of its constituent parts, the transporter can be heated to elevated temperatures and moved at these elevated temperatures with significantly reduced likelihood that the constituent moving parts will bind and interfere with one another as a result of thermal expansion upon reaching elevated temperatures. Furthermore, the transporter can be readily moved into and out of a furnace with significantly reduced likelihood of damage resulting from rapid temperature changes.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
Whenever possible, the same reference numbers will be used throughout the figures to refer to the same parts.